Antenna adaptation to manage the active set to manipulate soft hand-off regions

ABSTRACT

A method of managing the number of base station engaged in soft hand-off in a mobile communication system. The method involves manipulating a subscriber based directional antenna so as to control the number of base transceiver stations, pilot channels, beacon signals or other signals detected to be used in soft hand-off processing. The adaptive antennas are modified to manage the number of active set members, such as by manipulating direction, beamwidth, or other antenna parameters.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/386,392, filed Mar. 10, 2003, which claims the benefit of U.S.Provisional Application No. 60/363,227, filed on Mar. 8, 2002. Theentire teachings of the above application are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to managing the number of remote wirelesscommunication units that are performing hand-off, by using directionalantennas.

Many types of wireless communications systems such as cellular mobileradio telephone systems and emerging wireless data communication systemsprovide continuous radio coverage within a geographic area using anumber of fixed site transceivers such as base stations or wirelessaccess points. Continuous operation, or at least the appearance thereof,is maintained by automatic transfer, or “hand-off”, of a wirelessconnection from one site to another as a mobile unit travels around thearea.

In urban areas, and in locations with natural obstructions, it is commonfor radio signals to arrive at a receiver with reflections from nearbyobjects such as buildings or hills. This can occur along the so-calledforward direction, radio path from the fixed cite to the remote unitreceivers, as well as in a reverse direction, from the remote units tothe fixed site receivers. In either case, the received signal strengthcan vary substantially as a result of the terrain. Thus hand-offdecisions based on simple signal quality measurements do not necessarilyfollow the same boundaries as the designed cell site boundaries. Forexample, a remote unit located within the shadow of an obstructingbuilding produces a signal which has significantly decreased, as thoughthat remote unit has indeed traveled outside the cell. A hand-off wouldtherefore be typically initiated by the fixed site. A second hand-offprocess would again occur once the remote unit moves to a position clearof the obstruction. Indeed, it is as if cell boundaries are ratherindistinct.

Additional anomalies occur in other locations, such as at the top of ahill, where a particular mobile unit may be visible to many differentbase stations. In such position line of site propagation may beavailable for reliable connections to be made to several base stationscausing each such base station to begin to initiate soft hand-offprocedures with the single mobile unit.

In digital wireless communications systems, such as those based on CodeDivision Multiple Access (CDMA) modulation techniques (e.g. IS-95,IS-2000, W-CDMA, and the like), a soft hand-off procedure is used. Inthis procedure, each mobile unit simultaneously maintains a connectionwith two to three base stations. As the mobile unit moves from a currentcell (source cell) to the next cell (target cell) a traffic channelconnection is simultaneously maintained with both cell site basestations. On the forward link, the two signals are combined to yield acomposite signal of better reliability. On the reverse link, the mobileunit transmit signal is received by both cell site stations. The twocells demodulate the signals separately, sending the demodulated framesback to a centralized Mobile Switching Center (MSC). The MSC determinesthe best frame received out of the two that are sent back.

A so-called “softer” hand-off procedure occurs when a mobile unittransitions between two different sectors of the same cell. On theforward link, the mobile performs the same kind of combining process asfor soft hand-off. On the reverse link however, the signals from the twosectors are simultaneously received at the same cell site. The signalsare demodulated and combined inside the base station associated withthat cell, and only one frame is sent back to the MSC.

It is important to note that each sector in a CDMA system isdistinguished form the other sectors by a pilot channel code associatedwith that sector. The pilot channel signals are typically defined byshort Pseudo Noise (PN) codes with a specific code phase offset assignedto each sector. A pilot channel serves as a beacon for that sector, andthe associated base station aids the mobile in its acquiring otherlogical channels associated with that same sector.

In both soft hand-off and softer hand-off processing, the mobile unit isan intimate participant in the process. On requirement it has per theabove-mentioned standards is to constantly notify the base stationregarding its local propagation conditions, by sending Pilot SignalMeasurement Messages. The MSC may then make use of this information tomake hand-off decisions. This Mobile Assisted Hand-off (MAHO) processrequires that the mobile maintain in memory certain lists of basestation sectors identifiers and parameters. Sectors are identified inthe form of pilot channel identifiers for the sectors. The so-calledactive set list contains the pilot channel identifiers of those basestations or sectors that are actively communicating with the mobile. Ifthe active set contains more than one pilot channel, then that mobile ismaintaining multiple connections on separate traffic channels. In mostCDMA systems, the active set can contain up to six pilot channels. Apilot can only be added to the active set if the base stations send ahand-off direction message to the mobile and that message contains aparticular pilot channel to be added to the active set.

Soft hand-off capability has been a welcome advance in the field ofcellular communication since it encourages the seamless interconnectionsof calls as a mobile unit travels from sector to sector. However, softhand-off does not come without a price. While soft hand-off improves thereliability for users in weak signal conditions, such as when they arelocated on the boundary of a cell or in the shadow behind a building,unfortunately the technique also ends up being used in situations wheremany signals are available but where connection reliability is not anissue. For example, a mobile unit located on a tall hill may often havegood line of sight propagation to several base station sectors. However,using standard hand over processing, each visible sector will be addedto the active set, thus tying up traffic channels. This is despite thefact that each individual sector is alone sufficient to maintainreliable communications. However, soft hand-over procedures continue tobe utilized due to the fact that more than one sector can be seen by themobile unit.

In fact, wireless service providers have been making significant effortstowards eliminating excessive soft hand-off where they can find suchregions in their networks. They do this by periodically manipulating thepoint angle of base station antennas, the transmit power of base stationpower amplifiers and/or the height of antennas in the area adjacenthills. This optimization, which requires significant engineering byhuman beings, has a goal of increasing capacity by reducing the areas ofoverlapping signal coverage.

More information on soft hand-over procedures can be found in the bookby Yang, S. C. CDMA RF System Engineering (1998 Artec House, Inc.,Norwood, Mass.) pages 94-103.

SUMMARY OF THE INVENTION

The present invention relates to using an adaptive antenna such as adirectional antenna to provide increased capacity by manipulatingmeasurements made during a soft hand-off process. In particular, basestation or sector parameters as stored in an active set are firstcompared. A member of the active set is determined to have a very good,that is strong signal, and is labeled as a primary base station orsector. The other active set members are reduced and/or removed from theactive set through the expedient of manipulating the antenna settings.

More specifically, various criteria are used to determine thereliability of Base Transceiver Station (BTS) pilot channel signalsreceived from multiple base stations in the active set. A determinationis made if one, or a subset of these pilot signals, is sufficient tomaintain a reliable connection without the need for any of the others inthe set. Upon determining a list of unnecessary signals, the remoteantenna array is then manipulated by the mobile to reduce the strengthof one or more of the unnecessary pilot signals. This can beaccomplished for example by steering the antenna away from one or moreof the unnecessary pilot signals, and steering in the direction of oneof the primary pilot signals. It can also be done by broadening ornarrowing the beamwidth of the antenna.

The reliability of a particular member of the active set can bedetermined in a number of ways. In a preferred embodiment, this involvesmeasuring how close a signal is to a noise floor composed ofinterference from other sectors and thermal noise. Measurements on thepilot signal can include Received Signal Strength Indication (RSSI), acorrelated power (E_(c)) measurement, estimated noise based uponcalculations and/or estimated noise floor. Variations on these measureof signal strength, correlated power, or signal to noise ratio (SNR) maybe used.

Other refinements may be used. For example, if pilot signals arereceived from three base stations at approximately the same moderatereliability level, two of the base stations that are located in a samegeneral direction might be selected and the antenna steered in theirdirection. This will cause the third base station, which is in arelatively opposite direction, to be de-selected from the active set,even when its reliability or strength might be the same and/or slightlygreater than the other two pilot signals.

In further embodiments the process involves a step of forcing a patternchange to maintain an adequate number of members in the active set. Inparticular, when most or all of the active set are deemed to beunreliable, the antenna is steered in other directions. This cantypically cause additional pilot signals to become visible. These mayinclude new base stations signals of different or additional paths forthe currently active base station. The steering or re-steering of thearray typically continues until reliable signals are detected anddetermined.

Even in a situation where members of the active set are unreliable, butstill meet a lower, but sufficient quality metric, it may be desirableto keep the other base stations active. In this scenario a process canproceed as follows The array can be steered to a new position or patternwhile ensuring that the criteria for removing a base station from theactive set is not satisfied. This can be done typically by steering theantenna slightly away from its present state to cause a received signalto drop below a threshold for a predetermined duration of time(T_(drop)). If no better pilot channel is then added to the active set,an assumption can be made that the best candidates are still members ofthe active set.

In other aspects, if the number of stations in the active set isinsufficient, the pattern can be modified with a goal of adding newcandidate stations to the active set. For example, the antenna patternmay be modified, such as by broadening its beamwidth to permit thereception of additional pilot channel signals transmitted by other basestations in the area. The pattern can be broadened through a series ofsteps until a sufficient number of members are added to the active set.

In yet another aspect, specific directions or patterns can be furthermanipulated to reduce the list of active set members. For example, ifthe receiver has an adequate list of reliable connections, the beamwidth can be narrowed in order to keep the active set list to amanageable number.

As will be understood after the reading following detailed description,the present invention allows an increase in capacity of existing mobilewireless communication networks without changing infrastructure elementssuch as base transceiver stations, base station controllers, towers,access points, central antennas and the like. The only modificationsnecessary are made to the mobile subscriber units. For example,modifications can be made to wireless handset control chips and antennaswithout modifying cell site towers.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 illustrates a typical sector and cell site topology.

FIG. 2A shows typical overlap of sector coverage among three sectors andhow different active set assignments will occur for different mobileunit location.

FIG. 2B illustrates how the invention can be used to reduce the numberof active set members.

FIG. 3 is a more detailed view of an exemplary situation with a mobileunit making use of a directional antenna to reduce the members of anactive set.

FIG. 4 is a detailed flow chart of the active set qualification process.

FIG. 5 is a flow chart of operations performed when the number of activeset members is less than desired.

FIG. 6 is a flow chart of operations performed when there are aninsufficient number of reliable members in the active set.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A description of a preferred embodiment of the invention follows.

Turning attention now to the drawings, FIG. 1 illustrates an idealwireless network topology including cells and sectors. A specific regionin which wireless coverage is desired to be provided it is divided intosub-regions or cells. Radio equipment in each cell, known as a BaseTransceiver Station (BTS) is responsible for modulating and demobilitysignals, and making connections. The pattern is typical of a cellularcommunications system such as the IS-95 and CDMA 2000 mobile telephonesystems now prevalent in the United States that makes use of CodeDivision Multiple Access (CDMA) modulation. However, the pattern canalso be typical of other types of wireless networks such as WirelessLocal Area Networks (WLANs) and the like. In these systems, there stillis centrally located radio equipment, although it is known by othernames such as an “access point” or a “wireless hub”.

In the illustrated example, the antennas associated with BaseTransceiver Stations in each cell site are arranged into 120° sectors.The sectors are labels A, B, or C. Each of the cells is given an ordinalnumber in the figure, for example, 1, 2, 3, 4, 5, etc. Accordingly, eachsector has an associated number and letter, such as the sector label“3C”.

As a particular user moves from the coverage area of one sector to thecoverage area of another sector, a hand-off must occur to transition thecommunication link from one cell to the next. Most modem mobilecommunication systems support different types of hand-off processes.Common in CDMA systems is a so-called soft hand-off process. During thisprocess a mobile unit must simultaneously maintain connection with twoor three BTSs associated with, respectively, two or three sectors. Asthe mobile moves from its current cell to the next cell, a trafficchannel connection is simultaneously maintained with both cells. Thus,for example, a mobile unit moving from sector 3C to sector 7A willmaintain a connection with at least two BTSs. If the mobile unit shouldbe in a location adjacent where intersection with sector 5B occurs, aconnection will also be maintained with sector 5B as well.

For forward link communications, that is, from the BTS out to the remotemobile unit, the multiple signals are combined to yield a compositereceived signal of better quality. On the reverse link, that is, fortransmission from the mobile units back to the BTSs, the signal isreceived by the multiple BTSs. Each BTS needs to demodulate the signalseparately, sending the demodulated frames back to a Mobile SwitchingCenter (MSC). The MSC contains a selector that selects the best frameout of the two that are sent back.

Other processing, such as so-called soft hand-off processing, may alsotake place. This occurs when a mobile unit moves transitions between twodifferent sectors served by the same BTS. On a forward link, the mobilecan perform the same kind of combining process as it performed for softhand-off. In this case, the mobile uses its receiver processor tocombine signals received from two different sectors. On the reverselink, however, the same BTS will simultaneously receive two signals fromthe mobile unit. The two signals are demodulated and combined inside theBTS associated with the particular cell, and only one frame is sent backto the MSC.

Recent studies have shown that in a typical CDMA system, soft hand-offprocessing results in at least three channel connections typicallymaintained per active mobile unit. This figure includes a range ofusers, from those located close to the center of a cell (for which asingle connection is sufficient), to those located adjacent to theintersection of other cells. Such outlying mobile units need to maintainthree connections, one for each nearby sector, each connection using twoway softer hand-off channels, resulting in the possibility ofmaintaining as many as six simultaneous connections. These multipleconnections utilized in soft hand-off processing are maintain in a listin the mobile unit, known as the active set list.

FIG. 2A is a more detailed view of typical situation, showing howcoverages from three sectors may overlap in a region such as region 100of FIG. 1. Here a mobile unit 200 is located in an area adjacent to basestations 3C, 5B, and 7A. CDMA standards such as IS-95 and IS-2000 andthe like require that signals detected with sufficient energy bereported by the mobile unit 200 to the BTSs, and added to the activeset. In particular, these and similar systems, the mobile unit becomesan intimate participant in making decisions with regard to softhand-off. The mobile unit is required to constantly notify base stationsin its area regarding the local propagation conditions. The BTSs thenmake use of this information to make hand-off decisions.

More particularly, these Mobile Assisted Hand-Off (MAHO) proceduresrequire that the mobile unit 200 make a measurement of the forward linkenergy per chip with respect to a noise measurement (E_(c)/I_(o)) energyper chip measurement is with reference to the pseudo-noise sequence thatis used to spread the CDMA coded pilot channel signal. This pilotchannel measurement result must be then reported back to the basestation. Since each base station transmits its own pilot code on adifferent PN code offset, the E_(c)/I_(o) of a pilot channel gives agood indication of whether or not a particular sector is the bestcandidate to be the serving sector for a particular mobile unit 200.

In managing the hand-off process, the mobile unit 200 maintains in itsmemory a number of different lists of pilot channel measurements fordifferent base stations. This list, is the so-called the active set,contains an identification of the pilot channels of those sectors thatare actively communicating with the mobile unit on traffic channels. Ifthe active set contains only one pilot channel for example, then themobile is probably located close to the center of a cell and is notperforming soft hand-off. However, if the active set contains more thanone pilot channel, then the mobile 200 is maintaining a connection withall of those sectors on separate traffic channels.

In the standard processing the base station ultimately controls thehand-off process, because a pilot can only be added to the active set ifthe MSC sends a hand-off direction message to the mobile unit, with thatmessage containing the particular pilot to be added to the active set.

The mobile 200 also typically keeps other sets to manage the hand-offprocess. For example, a “candidate set” contains those pilots whoseenergy per chip are sufficient to make them future hand-off candidates.If the energy per chip of a detected pilot channel is greater than apilot detection threshold for a predetermined time period (T_(ADD)),then that pilot will be automatically added to the candidate set. Apilot is removed from this set and placed in the “neighbor set” if itsstrength drops below a pilot drop threshold, such as for more thanduration specified by a hand-off drop timer (T_(DROP)).

FIG. 2A is a typical situation. As can be seen from the plot, specificareas associated with coverage of a particular sector does not follow anexact 120° arc, but rather are modified by the surrounding naturaltopography. Mobile units located in areas labeled A (as shaded in thediagram) typically “see” only one base station and thus have only onesector listed in their active set. But, mobile units 200 located in theareas labeled B are within the range of two sectors, and thus will havetwo members in their active set. When a mobile unit is located in theregion labeled C, it may have three or possibly even more sectors listedin its active set, indicating that three or greater connections arebeing maintained for that mobile unit.

Soft hand-off processing greatly improves reliability for mobile unit inweak signal conditions. This may occur, for example, in the middle ofregion C, where hand-off is likely to occur between base stationsectors. However, mobile units in this location tend to utilize channelresources unnecessarily, even where reliability is not an issue. Forexample, mobiles located in most of region B may unnecessarily tie uptwo channels. If the region 100 was located on a tall hill where a lineof site propagation is very reliable and available to any of the 3C, 5B,and 7A, each sector will still be connected in soft hand-off utilizingtraffic channels. However, each individual signal would very well itselfbe enough to maintain reliable communication. In this situation, thechannel resources allocated to maintaining soft handover processing arenot related to any true requirement for maintaining reliablecommunications.

Indeed, in the past, the operators of wireless systems often putsignificant effort into eliminating the existence of B and C areas shownin FIG. 2A. They have done this by manipulating the pointing angle ofbase station sector antennas, reducing the transmit power of basestation amplifiers, and/or reducing the height of their transmitantennas. This optimization has a goal of increasing capacity byreducing the coverage area of individual sector BTS equipment. However,this requires much advanced engineering, for example, detailed knowledgeof the physical topology of the surrounding area, sophisticated softwaremodeling planning tools, and other field measurement resources. It wouldbe desirable if this situation could be improved automatically, bysomehow making modifications to the mobile unit 200 itself.

FIG. 2B illustrates an example of how the present invention can be usedto improve this situation, by simply adding a directional antenna to themobile unit 200 and slightly modifying the standard soft hand-offprocessing therein.

It can be appreciated that regions, associated with locations wherethree or more members in the active set have been eliminated entirely,and the area of region B with two candidates have been reduced markedly.

FIG. 3 will now be used to illustrate a more detailed description of apreferred embodiment of the invention to achieve a reduction in thenumber of members of the active set. FIG. 3, is in effect, a moredetailed view of the situation in area 100 adjacent where three sectors3C, 5B, and 7A converge. Each sector has an associated sector antenna120 and Base Transceiver Station (BTS) 130; the BTSs 130 are allconnected to a centralized Mobile Switching Center (MSC) 140 in a mannerthat is well known in the art. The BTSs 130 and MSC 140 cooperate withthe mobile unit 200 to perform Mobile Assisted Hand-Off (MAHO)procedures, as are well known in the art.

With the present invention however, the mobile unit 200 has associatedwith it a directional antenna array 220. The directional antenna 220,which may for example be a multi-element array, allows for the mobileunit to produce an antenna pattern 250 that has directional and/or othermodifiable characteristics. For example, a direction can be changed forthe antenna pattern 250 such that the mobile unit may point to any of anumber of directions around the 360° azimuth. In certain embodiments,other parameters of the antenna pattern 250, such as its beamwidth, W,can be modified.

More particularly, mobile unit 200 performs a process 260 to completevarious aspects of soft hand-off. In connection with this processing, aso-called active set list 300 is maintained. Here the active set 300 isa list containing the identifier of base station sectors presentlyvisible, such as determined by taking certain measurements on pilotsignals such as the aforementioned E_(c)/I_(o). This information,including a base station sector ID 301 and measurement energy value 302has been kept in the active list 300 associated in the prior art.

However, with the present invention, additional parameters are kept withthe active set 300. These may include for example, at least a “primary”indicator associated with one member of the active set, a reliabilitymeasure 304, and a quality indicator 305. The primary 303, reliability304, and quality indicator 305 can be single bit data values indicatingspecific additional information associated with each member of theactive set 300.

FIG. 4 is a flowchart of operations illustrating how the presentinvention can be used to control the operation of the sector antenna soas to reduce the number of members of the active set.

From an idle state 400, a first state 410 is entered in which thecontroller 260 manipulates the array 220 so as to have an initial broadbeamwidth setting. This step can, for example, set the array in anomni-directional mode. However, it should be understood that the initialstate here may not require an omni-directional (that is fully with 360°azimuthal coverage) but rather be some smaller angle, such as 120°.

In a next state 412, the active set list 300 is determined. This is donein a manner well known in the prior art, by detecting the existence ofvarious pilot channel signals in the vicinity of the handset 200(measuring their forward link E_(c)/I_(o)) and qualifying them to see ifthey pass a Pilot Detection Threshold for a period of time (T_(ADD)). Ata point when the qualification process is complete, those pilot signalspassing the qualification test are reported via a Pilot SignalMeasurement Message (PSMM) sent to the Network. This causes furthermessages to update the active set lists managed by the MSC.

At this point, however, according to the invention, the active set 300is examined to determine whether one or more primary pilot channels canbe identified. Thus, after using various criteria to determinereliability of the base pilot channel signals, a reliability measure isstored as reliability data 304. A received pilot signal's reliabilitymay be judged by one of many different methods. All of these measurestypically utilize a measure of how close that signal is to a noise floorcomposed of interference from other sectors and thermal noise. One suchmeasure may, for example, be Received Signal Strength Indication (RSSI)type measurement. However, correlated power, E_(c) may also be used byestimates of noise based upon actual measurement and/or estimatedcalculations may be used from these parameters a variation measure ofthe signal strength or correlated power can be used as a reliabilitymeasure. Other attempts to measure a signal to noise ratio may also beused to determine reliability.

In any event, after determining the reliability measures 304 associatedwith each of the pilot channels in the active set 300, one member of theactive set is chosen as the primary member.

In state 416, if the number of active set members is not greater thanthe number of desired members, a test is made. Specifically, if thenumber of active set members is only two, then perhaps no additionalprocessing is necessary and the process can terminate in state 418. Thisminimum number may be a fixed minimum number, but is preferablydetermined by the minimum number of active set members that result in adesired quality level. The minimum number is typically greater than one,to mitigate a fast fading situation.

However, if the test in state 416 indicates that three or more candidatemembers are in the active set, it is advantageous to perform additionalprocessing.

Specifically, in state 420 the antenna array in the mobile unit 220 isnow manipulated to optimize reception of a designated primary signal.For example, the array 220 can be modified by narrowing its beamwidth Wand/or changing its direction D to optimize reception of the pilotchannel that was designated as the primary. By steering the array inthis fashion, an effect will occur such that the signal power associatedwith the other pilot channels from other base station sectors will bereduced.

As shown in the particular example in FIG. 3, the active setqualification process 14 resulted in entries being made for each of thebase station channel sectors 3C, 5B, and 7A as members of the active set300. Each of these base station pilot channels was thus visible to themobile unit when it was in an omni-directional mode. However, upondetermining that reliability measure of base station sector 5B wasgreatest, the antenna array is manipulated to steer its pattern in thedirection of sector 5B, whereby signals received from sectors 3C and 7Aare now effectively attenuated.

Next, in step 422, with the array 122 set to an optimized reception forthe primary, requalification procedures are preformed on the active set.Specifically, measurements are again taken for members of the active setto see if they qualify to remain as members. In many instancestherefore, given that the antenna is now set to a directional mode andthat signals received from other sectors 3C and 7A are attenuated, theyare likely not to pass the T_(ADD) processing. They therefore should bereported as such to the MSC in a PSMM message, which will then causethem to be dropped from the active set. In state 424 the active set hasnow been reduced and processing can terminate in state 428.

In this manner it can be seen how these additional steps can be used todisqualify pilot channels that are no longer necessary for maintaining areliable connection. This frees up channel resources to be utilized byother mobile units.

In another embodiment, additional processing occurs as in FIG. 5, inorder to assure that at least a minimum number of members are alwaysassociated with the active set.

From an idle state 500, a test is periodically made to see if the numberof members of the active set is less than a number of desired members.If it is not, then the active set membership is adequate and this branchof processing can terminate in state 520. If, however, a minimum numberof active set members is not present, then processing will continue.This may occur if there are no members of the active set or only oneactive member, and it is desirable to determine if additional memberscan be added so that soft hand-off processing can be performed whenappropriate. In state 522, the antenna array parameters are adjusted (Wor D) so that additional base station transceivers D might be captured.This can be done by manipulating the direction or more probably thebeamwidth W of the antenna pattern 250. So, for example, the antennapattern might in state 522 be broadened to a beamwidth of 180°. Thiswill permit, in state 524, the detection of other pilot channels in thearea, pilot channels of both base stations 5B and 7A.

Thus, by forcing a change in the antenna pattern, a minimum number ofmembers can also be maintained in an active set 300. This can beadvantageous when the currently members are deemed unreliable, so thatby effectively or manipulating the antenna array, additional pilotchannel signals are visible.

FIG. 6 illustrates further processing that may be utilized. From an idlestate 600, a test is made in state 610 to determine if there are anyreliable members of the active set. If there are, then the active set ismaintained as in state 612 and processing of this branch terminates instate 614.

However, if there are no signals that meet a reliability test, then astate 620 is entered. Here, the array 120 is manipulated so thatadditional signals may be visible from the subscriber unit 200. Forexample, the array might be steered slightly in one direction or anotherfrom its present setting and/or its beamwidth slightly broadened. Thus,the antenna pattern is manipulated in such a way that it is possible tocapture additional base station pilot channels, but, without removingspecific pilot channel which is presently being utilized as the primaryactive set member. The net effect in this series of steps is this if acandidate angle for the array can be slightly changed, and result inincreased reliability for the currently members of the active set, thena higher quality signal will be received, and therefore performanceimproved.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. An apparatus for managing an active set of radio channels used insoft hand-off processing, a remote unit having an adaptive antenna,comprising: the remote unit configured to: determine an initial list ofmembers for the active set by detecting an existence of at least twopilot channel signals in a vicinity of the remote unit; make a change inan operating state of the adaptive antenna; and requalify the active setwith the changed adaptive antenna operating state.
 2. The apparatus ofclaim 1 wherein the adaptive antenna is a directional antenna array. 3.The apparatus of claim 2 wherein the adaptive antenna is a phased array.4. The apparatus of claim 3 wherein the adaptive antenna uses multiplereceivers and signal combiners.
 5. The remote unit of claim 1 furtherconfigured to: determine a reliability parameter for selecting membersof the active set; designate a selected one of the reliabilityparameters as sufficient to maintain a reliable connection; determinethat more than one active set member is a reliable connection; andchange operational state of the adaptive antenna to reduce a number ofradio channel signals received.
 6. A remote unit of claim 5 wherein themeasure of reliability is selected from a group consisting of receivedsignal strength indication, correlated power, and measurements of signalto noise ratio.
 7. The remote unit of claim 1, having a number ofmembers of the active set less than a desired number, configured to:adjust the antenna state to capture additional radio signals to bepossible members of the active set; and requalify the active setmembers.
 8. The remote unit of claim 1, wherein a member of the activeset is not reliable, configured to: select a new setting for theadaptive antenna; and requalify active set members.
 9. The remote unitof claim 1, having members of the active set deemed unreliable,configured to: steer the antenna such that additional radio signals aredetected.
 10. The remote unit of claim 1, where candidate pilot channelsignals are determined unreliable but of sufficient quality, isconfigured to: periodically select a new antenna operating state suchthat criteria for receiving at least one radio signal is not satisfied.